
    <%@ page contentType="image/JPEG"  
        import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"  
        pageEncoding="utf-8"%>  
    <%!Color getRandColor(int fc, int bc) {//给定范围获得随机颜色   
            Random random = new Random();   
            if (fc > 255)   
                fc = 255;   
            if (bc > 255)   
                bc = 255;   
            int r = fc + random.nextInt(bc - fc);   
            int g = fc + random.nextInt(bc - fc);   
            int b = fc + random.nextInt(bc - fc);   
            return new Color(r, g, b);   
        } 
        %>
    <%   
        //设置页面不缓存   
        response.setHeader("Pragma", "No-cache");   
        response.setHeader("Cache-Control", "no-cache");   
        response.setDateHeader("Expires", 0);        
        // 在内存中创建图象   
        int width = 60, height = 20;   
        BufferedImage image = new BufferedImage(width, height,   
                BufferedImage.TYPE_INT_RGB);         
        // 获取图形上下文   
        Graphics g = image.getGraphics();        
        //生成随机类   
        Random random = new Random();        
        // 设定背景色   
        g.setColor(getRandColor(200, 250));   
        g.fillRect(0, 0, width, height);        
        //设定字体   
        g.setFont(new Font("Times New Roman", Font.PLAIN, 18));         
        //画边框   
        //g.setColor(new Color());   
        //g.drawRect(0,0,width-1,height-1);   
      
        // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到   
        g.setColor(getRandColor(160, 200));   
        for (int i = 0; i < 100; i++) {   
            int x = random.nextInt(width);   
            int y = random.nextInt(height);   
            int xl = random.nextInt(12);   
            int yl = random.nextInt(12);   
            g.drawLine(x, y, x + xl, y + yl);   
        }   
      char[] code=new char[]{
      'A','B','C','D','E','F','G','H','I','J','K','L','M','N','P','Q','R','S','T','U','V','W','X','Y','Z',
      'a','b','c','d','e','f','g','h','i','j','k','l','m','n','p','q','r','s','t','u','v','w','x','y','z',
       '2','3','4','5','6','7','8','9'};
        // 取随机产生的认证码(4位数字)   
        String sRand = "";   
        for (int i = 0; i < 4; i++) {   
            String rand =String.valueOf(code[random.nextInt(code.length)]);   
            sRand += rand;   
            // 将认证码显示到图象中   
            g.setColor(new Color(20 + random.nextInt(110), 20 + random   
            .nextInt(110), 20 + random.nextInt(110)));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成   
            g.drawString(rand, 13 * i + 6, 16);   
        }        
        // 将认证码存入SESSION   
        session.setAttribute("verify", sRand);         
        // 图象生效   
        g.dispose();         
  
                // 输出图象到页面   
        ImageIO.write(image, "JPEG", response.getOutputStream());   
     
        out.clear();   
        out=pageContext.pushBody(); 
    %>  

